Inkjet printhead having selectively actuable nozzles arranged in nozzle pairs

ABSTRACT

An inkjet printhead includes a substrate having an array of nozzles grouped in nozzle pairs. Each nozzle pair has a common nozzle chamber and a single actuator configured to selectively eject ink from one or other of the nozzles in the nozzle pair.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No. 11/144,799 filed on Jun. 6, 2005, now issued U.S. Pat. No. 7,416,282, which is a continuation of U.S. application Ser. No. 10/882,772 filed on Jul. 2, 2004, now issued as U.S. Pat. No. 6,938,990, which is a continuation of U.S. application Ser. No. 10/302,604 filed on Nov. 23, 2002, now issued as U.S. Pat. No. 6,787,051, which is a continuation of U.S. application Ser. No. 09/112,801 filed on Jul. 10, 1998, now issued as U.S. Pat. No. 6,491,833, the entire contents of which are herein incorporated by reference.

The following Australian provisional patent applications are hereby incorporated by cross-reference. For the purposes of location and identification, US patent applications identified by their US patent application serial numbers (USSN) are listed alongside the Australian applications from which the US patent applications claim the right of priority. from which the US patents/patent applications claim the right of priority.

CROSS- US PATENT/PATENT REFERENCED APPLICATION AUSTRALIAN (CLAIMING RIGHT PROVISIONAL OF PRIORITY FROM PATENT AUSTRALIAN PROVISIONAL APPLICATION NO. APPLICATION) DOCKET NO. PO7991 6,750,901 ART01 PO8505 6,476,863 ART02 PO7988 6,788,336 ART03 PO9395 6,322,181 ART04 PO8017 6,597,817 ART06 PO8014 6,227,648 ART07 PO8025 6,727,948 ART08 PO8032 6,690,419 ART09 PO7999 6,727,951 ART10 PO8030 6,196,541 ART13 PO7997 6,195,150 ART15 PO7979 6,362,868 ART16 PO7978 6,831,681 ART18 PO7982 6,431,669 ART19 PO7989 6,362,869 ART20 PO8019 6,472,052 ART21 PO7980 6,356,715 ART22 PO8018 6,894,694 ART24 PO7938 6,636,216 ART25 PO8016 6,366,693 ART26 PO8024 6,329,990 ART27 PO7939 6,459,495 ART29 PO8501 6,137,500 ART30 PO8500 6,690,416 ART31 PO7987 7,050,143 ART32 PO8022 6,398,328 ART33 PO8497 7,110,024 ART34 PO8020 6,431,704 ART38 PO8504 6,879,341 ART42 PO8000 6,415,054 ART43 PO7934 6,665,454 ART45 PO7990 6,542,645 ART46 PO8499 6,486,886 ART47 PO8502 6,381,361 ART48 PO7981 6,317,192 ART50 PO7986 6,850,274 ART51 PO8026 6,646,757 ART53 PO8028 6,624,848 ART56 PO9394 6,357,135 ART57 PO9397 6,271,931 ART59 PO9398 6,353,772 ART60 PO9399 6,106,147 ART61 PO9400 6,665,008 ART62 PO9401 6,304,291 ART63 PO9403 6,305,770 ART65 PO9405 6,289,262 ART66 PP0959 6,315,200 ART68 PP1397 6,217,165 ART69 PP2370 6,786,420 DOT01 PO8003 6,350,023 Fluid01 PO8005 6,318,849 Fluid02 PO8066 6,227,652 IJ01 PO8072 6,213,588 IJ02 PO8040 6,213,589 IJ03 PO8071 6,231,163 IJ04 PO8047 6,247,795 IJ05 PO8035 6,394,581 IJ06 PO8044 6,244,691 IJ07 PO8063 6,257,704 IJ08 PO8057 6,416,168 IJ09 PO8056 6,220,694 IJ10 PO8069 6,257,705 IJ11 PO8049 6,247,794 IJ12 PO8036 6,234,610 IJ13 PO8048 6,247,793 IJ14 PO8070 6,264,306 IJ15 PO8067 6,241,342 IJ16 PO8001 6,247,792 IJ17 PO8038 6,264,307 IJ18 PO8033 6,254,220 IJ19 PO8002 6,234,611 IJ20 PO8068 6,302,528 IJ21 PO8062 6,283,582 IJ22 PO8034 6,239,821 IJ23 PO8039 6,338,547 IJ24 PO8041 6,247,796 IJ25 PO8004 6,557,977 IJ26 PO8037 6,390,603 IJ27 PO8043 6,362,843 IJ28 PO8042 6,293,653 IJ29 PO8064 6,312,107 IJ30 PO9389 6,227,653 IJ31 PO9391 6,234,609 IJ32 PP0888 6,238,040 IJ33 PP0891 6,188,415 IJ34 PP0890 6,227,654 IJ35 PP0873 6,209,989 IJ36 PP0993 6,247,791 IJ37 PP0890 6,336,710 IJ38 PP1398 6,217,153 IJ39 PP2592 6,416,167 IJ40 PP2593 6,243,113 IJ41 PP3991 6,283,581 IJ42 PP3987 6,247,790 IJ43 PP3985 6,260,953 IJ44 PP3983 6,267,469 IJ45 PO7935 6,224,780 IJM01 PO7936 6,235,212 IJM02 PO7937 6,280,643 IJM03 PO8061 6,284,147 IJM04 PO8054 6,214,244 IJM05 PO8065 6,071,750 IJM06 PO8055 6,267,905 IJM07 PO8053 6,251,298 IJM08 PO8078 6,258,285 IJM09 PO7933 6,225,138 IJM10 PO7950 6,241,904 IJM11 PO7949 6,299,786 IJM12 PO8060 6,866,789 IJM13 PO8059 6,231,773 IJM14 PO8073 6,190,931 IJM15 PO8076 6,248,249 IJM16 PO8075 6,290,862 IJM17 PO8079 6,241,906 IJM18 PO8050 6,565,762 IJM19 PO8052 6,241,905 IJM20 PO7948 6,451,216 IJM21 PO7951 6,231,772 IJM22 PO8074 6,274,056 IJM23 PO7941 6,290,861 IJM24 PO8077 6,248,248 IJM25 PO8058 6,306,671 IJM26 PO8051 6,331,258 IJM27 PO8045 6,110,754 IJM28 PO7952 6,294,101 IJM29 PO8046 6,416,679 IJM30 PO9390 6,264,849 IJM31 PO9392 6,254,793 IJM32 PP0889 6,235,211 IJM35 PP0887 6,491,833 IJM36 PP0882 6,264,850 IJM37 PP0874 6,258,284 IJM38 PP1396 6,312,615 IJM39 PP3989 6,228,668 IJM40 PP2591 6,180,427 IJM41 PP3990 6,171,875 IJM42 PP3986 6,267,904 IJM43 PP3984 6,245,247 IJM44 PP3982 6,315,914 IJM45 PP0895 6,231,148 IR01 PP0869 6,293,658 IR04 PP0887 6,614,560 IR05 PP0885 6,238,033 IR06 PP0884 6,312,070 IR10 PP0886 6,238,111 IR12 PP0877 6,378,970 IR16 PP0878 6,196,739 IR17 PP0883 6,270,182 IR19 PP0880 6,152,619 IR20 PO8006 6,087,638 MEMS02 PO8007 6,340,222 MEMS03 PO8010 6,041,600 MEMS05 PO8011 6,299,300 MEMS06 PO7947 6,067,797 MEMS07 PO7944 6,286,935 MEMS09 PO7946 6,044,646 MEMS10 PP0894 6,382,769 MEMS13

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

FIELD OF THE INVENTION

The present invention relates to the field of inkjet printing and, in particular, discloses a method of manufacturing a micro-electromechanical fluid ejecting device.

BACKGROUND OF THE INVENTION

Many ink jet printing mechanisms are known. Unfortunately, in mass production techniques, the production of ink jet heads is quite difficult. For example, often, the orifice or nozzle plate is constructed separately from the ink supply and ink ejection mechanism and bonded to the mechanism at a later stage (Hewlett-Packard Journal, Vol. 36 no 5, pp 33-37 (1985)). The separate material processing steps required in handling such precision devices often add a substantial expense in manufacturing.

Additionally, side shooting ink jet technologies (U.S. Pat. No. 4,899,181) are often used but again, this limits the amount of mass production throughput given any particular capital investment.

Additionally, more esoteric techniques are also often utilized. These can include electroforming of nickel stage (Hewlett-Packard Journal, Vol. 36 no 5, pp 33-37 (1985)), electro-discharge machining, laser ablation (U.S. Pat. No. 5,208,604), micro-punching, etc.

The utilization of the above techniques is likely to add substantial expense to the mass production of ink jet print heads and therefore add substantially to their final cost.

It would therefore be desirable if an efficient system for the mass production of ink jet print heads could be developed.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a method of manufacturing a Dual Chamber Single Vertical Actuator Ink Jet Printer print head wherein an array of nozzles are formed on a substrate utilizing planar monolithic deposition, lithographic and etching processes. Preferably, multiple ink jet heads are formed simultaneously on a single planar substrate such as a silicon wafer.

The print heads can be formed utilizing standard vlsi/ulsi processing and can include integrated drive electronics formed on the same substrate. The drive electronics preferably being of a CMOS type. In the final construction, ink can be ejected from the substrate substantially normal to the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic side view of an ink jet nozzle of the invention in a quiescent state;

FIG. 2 shows a schematic side view of the nozzle in an initial part of an ink ejection stage;

FIG. 3 shows a schematic side view of the nozzle in a further part of an ink ejection stage;

FIG. 4 shows a schematic side view of the nozzle in a final part of an ink ejection stage;

FIG. 5 shows a schematic side view of the nozzle again in its quiescent state;

FIG. 6 illustrates a side perspective view, of a single nozzle arrangement of the preferred embodiment.

FIG. 7 illustrates a perspective view, partly in section of a single nozzle arrangement of the preferred embodiment;

FIG. 8 shows a schematic side view of an initial stage in the manufacture of an ink jet nozzle of the invention with the deposition of a CMOS layer;

FIG. 9 shows a step of an initial etch to form a nozzle chamber;

FIG. 10 shows a step of depositing a first sacrificial layer;

FIG. 11 shows a step of etching the first sacrificial layer;

FIG. 12 shows a step of depositing a glass layer;

FIG. 13 shows a step of etching the glass layer;

FIG. 14 shows a step of depositing an actuator material layer;

FIG. 15 shows a step of planarizing the actuating material layers;

FIG. 16 shows a step of depositing a heater material layer;

FIG. 17 shows a step of depositing a further glass layer;

FIG. 18 shows a step of depositing a further heater material layer;

FIG. 19 shows a step of planarizing the further heater material layer;

FIG. 20 shows a step of depositing yet another glass layer;

FIG. 21 shows a step of etching said another glass layer;

FIG. 22 shows a step of etching the other glass layers;

FIG. 23 shows a step of depositing a further sacrificial layer;

FIG. 24 shows a step of forming a nozzle chamber;

FIG. 25 shows a step of forming nozzle openings;

FIG. 26 shows a step of back etching the substrate; and

FIG. 27 shows a final step of etching the sacrificial layers;

FIG. 28 illustrates a part of an array view of a portion of a printhead as constructed in accordance with the principles of the present invention;

FIG. 29 provides a legend of the materials indicated in FIGS. 30 to 42; and

FIG. 30 shows a sectional side view of an initial manufacturing step of an ink jet printhead nozzle showing a silicon wafer with a buried epitaxial layer and an electrical circuitry layer;

FIG. 31 shows a step of etching the oxide layer;

FIG. 32 shows a step of etching an exposed part of the silicon layer;

FIG. 33 shows a step of depositing a second sacrificial layer;

FIG. 34 shows a step of etching the first sacrificial layer;

FIG. 35 shows a step of etching the second sacrificial layer;

FIG. 36 shows the step of depositing a heater material layer;

FIG. 37 shows a step of depositing a further heater material layer;

FIG. 38 shows a step of etching a glass layer;

FIG. 39 shows a step of depositing a further glass layer;

FIG. 40 shows a step of etching the further glass layer;

FIG. 41 shows a step of further etching the further glass layer;

FIG. 42 shows a step of back etching through the silicon layer;

FIG. 43 shows a step of etching the sacrificial layers; and

FIG. 44 shows a step of filling the completed ink jet nozzle with ink.—

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment, there is provided an inkjet printhead having an array of nozzles wherein the nozzles are grouped in pairs and each pair is provided with a single actuator which is actuated so as to move a paddle type mechanism to force the ejection of ink out of one or other of the nozzle pairs. The paired nozzles eject ink from a single nozzle chamber which is re-supplied by means of an ink supply channel. Further, the actuator of the preferred embodiment has unique characteristics so as to simplify the actuation process.

Turning initially to FIGS. 1 to 5, there will now be explained the principles of operation of the preferred embodiment. In the preferred embodiment, a single nozzle chamber 1 is utilized to supply ink to two ink ejection nozzles 2, 3. Ink is re-supplied to the nozzle chamber 1 via means of an ink supply channel 5. In its quiescent position, two ink menisci 6, 7 are formed around the ink ejection holes 2, 3. The arrangement of FIG. 1 being substantially axially symmetric around a central paddle 9 which is attached to an actuator mechanism.

When it is desired to eject ink out of one of the nozzles, say nozzle 3, the paddle 9 is actuated so that it begins to move as indicated in FIG. 2. The movement of paddle 9 in the direction 10 results in a general compression of the ink on the right hand side of the paddle 9. The compression of the ink results in the meniscus 7 growing as the ink is forced out of the nozzles 3. Further, the meniscus 6 undergoes an inversion as the ink is sucked back on the left hand side of the actuator 10 with additional ink 12 being sucked in from ink supply channel 5. The paddle actuator 9 eventually comes to rest and begins to return as illustrated in FIG. 3. The ink 13 within meniscus 7 has substantial forward momentum and continues away from the nozzle chamber whilst the paddle 9 causes ink to be sucked back into the nozzle chamber. Further, the surface tension on the meniscus 6 results in further in flow of the ink via the ink supply channel 5. The resolution of the forces at work in the resultant flows results in a general necking and subsequent breaking of the meniscus 7 as illustrated in FIG. 4 wherein a drop 14 is formed which continues onto the media or the like. The paddle 9 continues to return to its quiescent position.

Next, as illustrated in FIG. 5, the paddle 9 returns to its quiescent position and the nozzle chamber refills by means of surface tension effects acting on meniscuses 6, 7 with the arrangement of returning to that showing in FIG. 1. When required, the actuator 9 can be activated to eject ink out of the nozzle 2 in a symmetrical manner to that described with reference to FIGS. 1-5. Hence, a single actuator 9 is activated to provide for ejection out of multiple nozzles. The dual nozzle arrangement has a number of advantages including in that movement of actuator 9 does not result in a significant vacuum forming on the back surface of the actuator 9 as a result of its rapid movement. Rather, meniscus 6 acts to ease the vacuum and further acts as a “pump” for the pumping of ink into the nozzle chamber. Further, the nozzle chamber is provided with a lip 15 (FIG. 2) which assists in equalizing the increase in pressure around the ink ejection holes 3 which allows for the meniscus 7 to grow in an actually symmetric manner thereby allowing for straight break off of the drop 14.

Turning now to FIGS. 6 and 7, there is illustrated a suitable nozzle arrangement with FIG. 6 showing a single side perspective view and FIG. 7 showing a view, partly in section illustrating the nozzle chamber. The actuator 20 includes a pivot arm attached at the post 21. The pivot arm includes an internal core portion 22 which can be constructed from glass. On each side 23, 24 of the internal portion 22 is two separately control heater arms which can be constructed from an alloy of copper and nickel (45% copper and 55% nickel). The utilization of the glass core is advantageous in that it has a low coefficient thermal expansion and coefficient of thermal conductivity. Hence, any energy utilized in the heaters 23, 24 is substantially maintained in the heater structure and utilized to expand the heater structure and opposed to an expansion of the glass core 22. Structure or material chosen to form part of the heater structure preferably has a high “bend efficiency”. One form of definition of bend efficiency can be the Young's modulus times the coefficient of thermal expansion divided by the density and by the specific heat capacity.

The copper nickel alloy in addition to being conductive has a high coefficient of thermal expansion, a low specific heat and density in addition to a high Young's modulus. It is therefore a highly suitable material for construction of the heater element although other materials would also be suitable.

Each of the heater elements can comprise a conductive out and return trace with the traces being insulated from one and other along the length of the trace and conductively joined together at the far end of the trace. The current supply for the heater can come from a lower electrical layer via the pivot anchor 21. At one end of the actuator 20, there is provided a bifurcated portion 30 which has attached at one end thereof to leaf portions 31, 32.

To operate the actuator, one of the arms 23, 24 e.g. 23 is heated in air by passing current through it. The heating of the arm results in a general expansion of the arm. The expansion of the arm results in a general bending of the arm 20. The bending of the arm 20 further results in leaf portion 32 pulling on the paddle portion 9. The paddle 9 is pivoted around a fulcrum point by means of attachment to leaf portions 38, 39 which are generally thin to allow for minor flexing. The pivoting of the arm 9 causes ejection of ink from the nozzle hole 40. The heater is deactivated resulting in a return of the actuator 20 to its quiescent position and its corresponding return of the paddle 9 also to is quiescent position. Subsequently, to eject ink out of the other nozzle hole 41, the heater 24 can be activated with the paddle operating in a substantially symmetric manner.

It can therefore be seen that the actuator can be utilized to move the paddle 9 on demand so as to eject drops out of the ink ejection hole e.g. 40 with the ink refilling via an ink supply channel 44 located under the paddle 9.

The nozzle arrangement of the preferred embodiment can be formed on a silicon wafer utilizing standard semi-conductor fabrication processing steps and micro-electromechanical systems (MEMS) construction techniques.

For a general introduction to a micro-electro mechanical system (MEMS) reference is made to standard proceedings in this field including the proceeding of the SPIE (International Society for Optical Engineering) including volumes 2642 and 2882 which contain the proceedings of recent advances and conferences in this field.

Preferably, a large wafer of printheads is constructed at any one time with each printhead providing a predetermined pagewidth capabilities and a single printhead can in turn comprise multiple colors so as to provide for full color output as would be readily apparent to those skilled in the art.

Turning now to FIG. 8-FIG. 27 there will now be explained one form of fabrication of the preferred embodiment. The preferred embodiment can start as illustrated in FIG. 8 with a CMOS processed silicon wafer 50 which can include a standard CMOS layer 51 including of the relevant electrical circuitry etc. The processing steps can then be as follows:

-   1. As illustrated in FIG. 9, a deep etch of the nozzle chamber 98 is     performed to a depth of 25 micron; -   2. As illustrated in FIG. 10, a 27 micron layer of sacrificial     material 52 such as aluminum is deposited; -   3. As illustrated in FIG. 11, the sacrificial material is etched to     a depth of 26 micron using a glass stop so as to form cavities using     a paddle and nozzle mask. -   4. As illustrated in FIG. 12, a 2 micron layer of low stress glass     53 is deposited. -   5. As illustrated in FIG. 13, the glass is etched to the aluminum     layer utilizing a first heater via mask. -   6. As illustrated in FIG. 14, a 2-micron layer of 60% copper and 40%     nickel is deposited 55 and planarized (FIG. 15) using chemical     mechanical planarization (CMP). -   7. As illustrated in FIG. 16, a 0.1 micron layer of silicon nitride     is deposited 56 and etched using a heater insulation mask. -   8. As illustrated in FIG. 17, a 2-micron layer of low stress glass     57 is deposited and etched using a second heater mask. -   9. As illustrated in FIG. 18, a 2-micron layer of 60% copper and 40%     nickel 58 is deposited and planarized (FIG. 19) using chemical     mechanical planarization. -   10. As illustrated in FIG. 20, a 1-micron layer of low stress glass     60 is deposited and etched (FIG. 21) using a nozzle wall mask. -   11. As illustrated in FIG. 22, the glass is etched down to the     sacrificial layer using an actuator paddle wall mask. -   12. As illustrated in FIG. 23, a 5-micron layer of sacrificial     material 62 is deposited and planarized using CMP. -   13. As illustrated in FIG. 24, a 3-micron layer of low stress glass     63 is deposited and etched using a nozzle rim mask. -   14. As illustrated in FIG. 25, the glass is etched down to the     sacrificial layer using nozzle mask. -   15. As illustrated in FIG. 26, the wafer can be etched from the back     using a deep silicon trench etcher such as the Silicon Technology     Systems deep trench etcher. -   16. Finally, as illustrated in FIG. 27, the sacrificial layers are     etched away releasing the ink jet structure.

Subsequently, the print head can be washed, mounted on an ink chamber, relevant electrical interconnections TAB bonded and the print head tested.

Turning now to FIG. 28, there is illustrated a portion 80 of a full color printhead which is divided into three series of nozzles 71, 72 and 73. Each series can supply a separate color via means of a corresponding ink supply channel. Each series is further subdivided into two sub rows e.g. 76, 77 with the relevant nozzles of each sub row being fired simultaneously with one sub row being fired a predetermined time after a second sub row such that a line of ink drops is formed on a page.

As illustrated in FIG. 28 the actuators are formed in a curved relationship with respect to the main nozzle access so as to provide for a more compact packing of the nozzles. Further, the block portion (21 of FIG. 6) is formed in the wall of an adjacent series with the block portion of the row 73 being formed in a separate guide rail 80 provided as an abutment surface for the TAB strip when it is abutted against the guide rail 80 so as to provide for an accurate registration of the tab strip with respect to the bond pads 81, 82 which are provided along the length of the printhead so as to provide for low impedance driving of the actuators.

The principles of the preferred embodiment can obviously be readily extended to other structures. For example, a fulcrum arrangement could be constructed which includes two arms which are pivoted around a thinned wall by means of their attachment to a cross bar. Each arm could be attached to the central cross bar by means of similarly leafed portions to that shown in FIG. 6 and FIG. 7. The distance between a first arm and the thinned wall can be L units whereas the distance between the second arm and wall can be NL units. Hence, when a translational movement is applied to the second arm for a distance of N×X units the first arm undergoes a corresponding movement of X units. The leafed portions allow for flexible movement of the arms whilst providing for full pulling strength when required.

It would be evident to those skilled in the art that the present invention can further be utilized in either mechanical arrangement requiring the application forces to induce movement in a structure.

One form of detailed manufacturing process which can be used to fabricate monolithic ink jet print heads operating in accordance with the principles taught by the present embodiment can proceed utilizing the following steps:

-   1. Using a double sided polished wafer 50, complete drive     transistors, data distribution, and timing circuits using a 0.5     micron, one poly, 2 metal CMOS process 51. Relevant features of the     wafer at this step are shown in FIG. 30. For clarity, these diagrams     may not be to scale, and may not represent a cross section though     any single plane of the nozzle. FIG. 29 is a key to representations     of various materials in these manufacturing diagrams, and those of     other cross-referenced ink jet configurations. -   2. Etch oxide down to silicon or aluminum using Mask 1. This mask     defines the ink inlet, the heater contact vias, and the edges of the     print head chips. This step is shown in FIG. 31. -   3. Etch exposed silicon 51 to a depth of 20 microns. This step is     shown in FIG. 32. -   4. Deposit a 1-micron conformal layer of a first sacrificial     material 91. -   5. Deposit 20 microns of a second sacrificial material 92, and     planarize down to the first sacrificial layer using CMP. This step     is shown in FIG. 33. -   6. Etch the first sacrificial layer using Mask 2, defining the     nozzle chamber wall 93, the paddle 9, and the actuator anchor point     21. This step is shown in FIG. 34. -   7. Etch the second sacrificial layer down to the first sacrificial     layer using Mask 3. This mask defines the paddle 9. This step is     shown in FIG. 35. -   8. Deposit a 1-micron conformal layer of PECVD glass 53. -   9. Etch the glass using Mask 4, which defines the lower layer of the     actuator loop. -   10. Deposit 1 micron of heater material 55, for example titanium     nitride (TiN) or titanium diboride (TiB2). Planarize using CMP. This     step is shown in FIG. 36. -   11. Deposit 0.1 micron of silicon nitride 56. -   12. Deposit 1 micron of PECVD glass 57. -   13. Etch the glass using Mask 5, which defines the upper layer of     the actuator loop. -   14. Etch the silicon nitride using Mask 6, which defines the vias     connecting the upper layer of the actuator loop to the lower layer     of the actuator loop. -   15. Deposit 1 micron of the same heater material 58 previously     deposited. Planarize using CMP. This step is shown in FIG. 37. -   16. Deposit 1 micron of PECVD glass 60. -   17. Etch the glass down to the sacrificial layer using Mask 6. This     mask defines the actuator and the nozzle chamber wall, with the     exception of the nozzle chamber actuator slot. This step is shown in     FIG. 38. -   18. Wafer probe. All electrical connections are complete at this     point, bond pads are accessible, and the chips are not yet     separated. -   19. Deposit 4 microns of sacrificial material 62 and planarize down     to glass using CMP. -   20. Deposit 3 microns of PECVD glass 63. This step is shown in FIG.     39. -   21. Etch to a depth of (approx.) 1 micron using Mask 7. This mask     defines the nozzle rim 95. This step is shown in FIG. 40. -   22. Etch down to the sacrificial layer using Mask 8. This mask     defines the roof of the nozzle chamber, and the nozzle 40, 41     itself. This step is shown in FIG. 41. -   23. Back-etch completely through the silicon wafer (with, for     example, an ASE Advanced Silicon Etcher from Surface Technology     Systems) using Mask 9. This mask defines the ink inlets 65 which are     etched through the wafer. The wafer is also diced by this etch. This     step is shown in FIG. 42. -   24. Etch both types of sacrificial material. The nozzle chambers are     cleared, the actuators freed, and the chips are separated by this     etch. This step is shown in FIG. 43. -   25. Mount the print heads in their packaging, which may be a molded     plastic former incorporating ink channels which supply the     appropriate color ink 96 to the ink inlets at the back of the wafer. -   26. Connect the print heads to their interconnect systems. For a low     profile connection with minimum disruption of airflow, TAB may be     used. Wire bonding may also be used if the printer is to be operated     with sufficient clearance to the paper. -   27. Hydrophobize the front surface of the print heads. -   28. Fill the completed print heads with ink and test them. A filled     nozzle is shown in FIG. 44.

The presently disclosed ink jet printing technology is potentially suited to a wide range of printing system including: color and monochrome office printers, short run digital printers, high speed digital printers, offset press supplemental printers, low cost scanning printers high speed pagewidth printers, notebook computers with in-built pagewidth printers, portable color and monochrome printers, color and monochrome copiers, color and monochrome facsimile machines, combined printer, facsimile and copying machines, label printers, large format plotters, photograph copiers, printers for digital photographic “minilabs”, video printers, PhotoCD printers, portable printers for PDAs, wallpaper printers, indoor sign printers, billboard printers, fabric printers, camera printers and fault tolerant commercial printer arrays.

It would be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Of course many different devices could be used. However presently popular ink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption. This is approximately 100 times that required for high speed, and stems from the energy-inefficient means of drop ejection. This involves the rapid boiling of water to produce a vapor bubble which expels the ink. Water has a very high heat capacity, and must be superheated in thermal ink jet applications. This leads to an efficiency of around 0.02%, from electricity input to drop momentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size and cost. Piezoelectric crystals have a very small deflection at reasonable drive voltages, and therefore require a large area for each nozzle. Also, each piezoelectric actuator must be connected to its drive circuit on a separate substrate. This is not a significant problem at the current limit of around 300 nozzles per print head, but is a major impediment to the fabrication of pagewidth print heads with 19,200 nozzles.

Ideally, the ink jet technologies used meet the stringent requirements of in-camera digital color printing and other high quality, high speed, low cost printing applications. To meet the requirements of digital photography, new ink jet technologies have been created. The target features include:

low power (less than 10 Watts)

High-resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systems described below with differing levels of difficulty. Forty-five different ink jet technologies have been developed by the Assignee to give a wide range of choices for high volume manufacture. These technologies form part of separate applications assigned to the present Assignee as set out in the table above under the heading Cross References to Related Applications.

The ink jet designs shown here are suitable for a wide range of digital printing systems, from battery powered one-time use digital cameras, through to desktop and network printers, and through to commercial printing systems

For ease of manufacture using standard process equipment, the print head is designed to be a monolithic 0.5-micron CMOS chip with MEMS post processing. For color photographic applications, the print head is 100 mm long, with a width which depends upon the ink jet type. The smallest print head designed is IJ38, which is 0.35 mm wide, giving a chip area of 35 square mm. The print heads each contain 19,200 nozzles plus data and control circuitry.

Ink is supplied to the back of the print head by injection molded plastic ink channels. The molding requires 50-micron features, which can be created using a lithographically micro machined insert in a standard injection-molding tool Ink flows through holes etched through the wafer to the nozzle chambers fabricated on the front surface of the wafer. The print head is connected to the camera circuitry by tape automated bonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation of individual ink jet nozzles have been identified. These characteristics are largely orthogonal, and so can be elucidated as an eleven dimensional matrix. Most of the eleven axes of this matrix include entries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of ink jet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types) Nozzle clearing method (9 types) Nozzle plate construction (9 types) Drop ejection direction (5 types) Ink type (7 types)

The complete eleven dimensional table represented by these axes contains 36.9 billion possible configurations of ink jet nozzle. While not all of the possible combinations result in a viable ink jet technology, many million configurations are viable. It is clearly impractical to elucidate all of the possible configurations. Instead, certain ink jet types have been investigated in detail. These are designated IJ01 to IJ45 which matches the docket numbers in the table under the heading CROSS REFERENCES TO RELATED APPLICATIONS.

Other ink jet configurations can readily be derived from these forty-five examples by substituting alternative configurations along one or more of the 11 axes. Most of the IJ01 to IJ45 examples can be made into ink jet print heads with characteristics superior to any currently available ink jet technology.

Where there are prior art examples known to the inventor, one or more of these examples are listed in the examples column of the tables below. The IJ01 to IJ45 series are also listed in the examples column. In some cases, a printer may be listed more than once in a table, where it shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Home printers, Office network printers, Short run digital printers, Commercial print systems, Fabric printers, Pocket printers, Internet WWW printers, Video printers, Medical imaging, Wide format printers, Notebook PC printers, Fax machines, Industrial printing systems, Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrix is set out in the following tables.

Description Advantages Disadvantages Examples ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) Thermal An electrothermal Large force High power Canon Bubblejet bubble heater heats the ink to generated Ink carrier limited 1979 Endo et al GB above boiling point, Simple to water patent 2,007,162 transferring significant construction Low efficiency Xerox heater-in- heat to the aqueous No moving parts High pit 1990 Hawkins et ink. A bubble Fast operation temperatures al U.S. Pat. No. 4,899,181 nucleates and quickly Small chip area required Hewlett-Packard forms, expelling the required for actuator High mechanical TIJ 1982 Vaught et ink. stress al U.S. Pat. No. 4,490,728 The efficiency of the Unusual materials process is low, with required typically less than Large drive 0.05% of the electrical transistors energy being Cavitation causes transformed into actuator failure kinetic energy of the Kogation reduces drop. bubble formation Large print heads are difficult to fabricate Piezo- A piezoelectric crystal Low power Very large area Kyser et al U.S. Pat. No. electric such as lead consumption required for actuator 3,946,398 lanthanum zirconate Many ink types Difficult to Zoltan U.S. Pat. No. (PZT) is electrically can be used integrate with 3,683,212 activated, and either Fast operation electronics 1973 Stemme expands, shears, or High efficiency High voltage U.S. Pat. No. 3,747,120 bends to apply drive transistors Epson Stylus pressure to the ink, required Tektronix ejecting drops. Full pagewidth IJ04 print heads impractical due to actuator size Requires electrical poling in high field strengths during manufacture Electro- An electric field is Low power Low maximum Seiko Epson, strictive used to activate consumption strain (approx. Usui et all JP electrostriction in Many ink types 0.01%) 253401/96 relaxor materials such can be used Large area IJ04 as lead lanthanum Low thermal required for actuator zirconate titanate expansion due to low strain (PLZT) or lead Electric field Response speed is magnesium niobate strength required marginal (~10 μs) (PMN). (approx. 3.5 V/μm) High voltage can be generated drive transistors without difficulty required Does not require Full pagewidth electrical poling print heads impractical due to actuator size Ferro- An electric field is Low power Difficult to IJ04 electric used to induce a phase consumption integrate with transition between the Many ink types electronics antiferroelectric (AFE) can be used Unusual materials and ferroelectric (FE) Fast operation such as PLZSnT are phase. Perovskite (<1 μs) required materials such as tin Relatively high Actuators require modified lead longitudinal strain a large area lanthanum zirconate High efficiency titanate (PLZSnT) Electric field exhibit large strains of strength of around 3 V/μm up to 1% associated can be readily with the AFE to FE provided phase transition. Electro- Conductive plates are Low power Difficult to IJ02, IJ04 static separated by a consumption operate electrostatic plates compressible or fluid Many ink types devices in an dielectric (usually air). can be used aqueous Upon application of a Fast operation environment voltage, the plates The electrostatic attract each other and actuator will displace ink, causing normally need to be drop ejection. The separated from the conductive plates may ink be in a comb or Very large area honeycomb structure, required to achieve or stacked to increase high forces the surface area and High voltage therefore the force. drive transistors may be required Full pagewidth print heads are not competitive due to actuator size Electro- A strong electric field Low current High voltage 1989 Saito et al, static pull is applied to the ink, consumption required U.S. Pat. No. 4,799,068 on ink whereupon Low temperature May be damaged 1989 Miura et al, electrostatic attraction by sparks due to air U.S. Pat. No. 4,810,954 accelerates the ink breakdown Tone-jet towards the print Required field medium. strength increases as the drop size decreases High voltage drive transistors required Electrostatic field attracts dust Permanent An electromagnet Low power Complex IJ07, IJ10 magnet directly attracts a consumption fabrication electro- permanent magnet, Many ink types Permanent magnetic displacing ink and can be used magnetic material causing drop ejection. Fast operation such as Neodymium Rare earth magnets High efficiency Iron Boron (NdFeB) with a field strength Easy extension required. around 1 Tesla can be from single nozzles High local used. Examples are: to pagewidth print currents required Samarium Cobalt heads Copper (SaCo) and magnetic metalization should materials in the be used for long neodymium iron boron electromigration family (NdFeB, lifetime and low NdDyFeBNb, resistivity NdDyFeB, etc) Pigmented inks are usually infeasible Operating temperature limited to the Curie temperature (around 540 K) Soft A solenoid induced a Low power Complex IJ01, IJ05, IJ08, magnetic magnetic field in a soft consumption fabrication IJ10, IJ12, IJ14, core magnetic core or yoke Many ink types Materials not IJ15, IJ17 electro- fabricated from a can be used usually present in a magnetic ferrous material such Fast operation CMOS fab such as as electroplated iron High efficiency NiFe, CoNiFe, or alloys such as CoNiFe Easy extension CoFe are required [1], CoFe, or NiFe from single nozzles High local alloys. Typically, the to pagewidth print currents required soft magnetic material heads Copper is in two parts, which metallisation should are normally held be used for long apart by a spring. electromigration When the solenoid is lifetime and low actuated, the two parts resistivity attract, displacing the Electroplating is ink. required High saturation flux density is required (2.0-2.1 T is achievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force acts as a IJ06, IJ11, IJ13, force acting on a current consumption twisting motion IJ16 carrying wire in a Many ink types Typically, only a magnetic field is can be used quarter of the utilized. Fast operation solenoid length This allows the High efficiency provides force in a magnetic field to be Easy extension useful direction supplied externally to from single nozzles High local the print head, for to pagewidth print currents required example with rare heads Copper earth permanent metallisation should magnets. be used for long Only the current electro migration carrying wire need be lifetime and low fabricated on the print resistivity head, simplifying Pigmented inks materials are usually requirements. infeasible Magneto- The actuator uses the Many ink types Force acts as a Fischenbeck, U.S. Pat. No. striction giant magnetostrictive can be used twisting motion 4,032,929 effect of materials Fast operation Unusual materials IJ25 such as Terfenol-D (an Easy extension such as Terfenol-D alloy of terbium, from single nozzles are required dysprosium and iron to pagewidth print High local developed at the Naval heads currents required Ordnance Laboratory, High force is Copper hence Ter-Fe-NOL). available metallisation should For best efficiency, the be used for long actuator should be pre- electro migration stressed to approx. 8 MPa. lifetime and low resistivity Pre-stressing may be required Surface Ink under positive Low power Requires Silverbrook, EP tension pressure is held in a consumption supplementary force 0771 658 A2 and reduction nozzle by surface Simple to effect drop related patent tension. The surface construction separation applications tension of the ink is No unusual Requires special reduced below the materials required in ink surfactants bubble threshold, fabrication Speed may be causing the ink to High efficiency limited by surfactant egress from the Easy extension properties nozzle. from single nozzles to pagewidth print heads Viscosity The ink viscosity is Simple Requires Silverbrook, EP reduction locally reduced to construction supplementary force 0771 658 A2 and select which drops are No unusual to effect drop related patent to be ejected. A materials required in separation applications viscosity reduction can fabrication Requires special be achieved Easy extension ink viscosity electrothermally with from single nozzles properties most inks, but special to pagewidth print High speed is inks can be engineered heads difficult to achieve for a 100:1 viscosity Requires reduction. oscillating ink pressure A high temperature difference (typically 80 degrees) is required Acoustic An acoustic wave is Can operate Complex drive 1993 Hadimioglu generated and without a nozzle circuitry et al, EUP 550,192 focussed upon the plate Complex 1993 Elrod et al, drop ejection region. fabrication EUP 572,220 Low efficiency Poor control of drop position Poor control of drop volume Thermo- An actuator which Low power Efficient aqueous IJ03, IJ09, IJ17, elastic relies upon differential consumption operation requires a IJ18, IJ19, IJ20, bend thermal expansion Many ink types thermal insulator on IJ21, IJ22, IJ23, actuator upon Joule heating is can be used the hot side IJ24, IJ27, IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabrication prevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35, IJ36, IJ37, required for each Pigmented inks IJ38, IJ39, IJ40, actuator may be infeasible, IJ41 Fast operation as pigment particles High efficiency may jam the bend CMOS actuator compatible voltages and currents Standard MEMS processes can be used Easy extension from single nozzles to pagewidth print heads High CTE A material with a very High force can be Requires special IJ09, IJ17, IJ18, thermo- high coefficient of generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermal expansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator (CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30, polytetrafluoroethylene under development: which is not yet IJ31, IJ42, IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTE materials deposition (CVD), fabs are usually non- spin coating, and PTFE deposition conductive, a heater evaporation cannot be followed fabricated from a PTFE is a with high conductive material is candidate for low temperature (above incorporated. A 50 μm dielectric constant 350° C.) processing long PTFE bend insulation in ULSI Pigmented inks actuator with Very low power may be infeasible, polysilicon heater and consumption as pigment particles 15 mW power input Many ink types may jam the bend can provide 180 μN can be used actuator force and 10 μm Simple planar deflection. Actuator fabrication motions include: Small chip area Bend required for each Push actuator Buckle Fast operation Rotate High efficiency CMOS compatible voltages and currents Easy extension from single nozzles to pagewidth print heads Conductive A polymer with a high High force can be Requires special IJ24 polymer coefficient of thermal generated materials thermo- expansion (such as Very low power development (High elastic PTFE) is doped with consumption CTE conductive actuator conducting substances Many ink types polymer) to increase its can be used Requires a PTFE conductivity to about Simple planar deposition process, 3 orders of magnitude fabrication which is not yet below that of copper. Small chip area standard in ULSI The conducting required for each fabs polymer expands actuator PTFE deposition when resistively Fast operation cannot be followed heated. High efficiency with high Examples of CMOS temperature (above conducting dopants compatible voltages 350° C.) processing include: and currents Evaporation and Carbon nanotubes Easy extension CVD deposition Metal fibers from single nozzles techniques cannot Conductive polymers to pagewidth print be used such as doped heads Pigmented inks polythiophene may be infeasible, Carbon granules as pigment particles may jam the bend actuator Shape A shape memory alloy High force is Fatigue limits IJ26 memory such as TiNi (also available (stresses maximum number alloy known as Nitinol - of hundreds of of cycles Nickel Titanium alloy MPa) Low strain (1%) developed at the Naval Large strain is is required to extend Ordnance Laboratory) available (more than fatigue resistance is thermally switched 3%) Cycle rate limited between its weak High corrosion by heat removal martensitic state and resistance Requires unusual its high stiffness Simple materials (TiNi) austenic state. The construction The latent heat of shape of the actuator Easy extension transformation must in its martensitic state from single nozzles be provided is deformed relative to to pagewidth print High current the austenitic shape. heads operation The shape change Low voltage Requires pre- causes ejection of a operation stressing to distort drop. the martensitic state Linear Linear magnetic Linear Magnetic Requires unusual IJ12 Magnetic actuators include the actuators can be semiconductor Actuator Linear Induction constructed with materials such as Actuator (LIA), Linear high thrust, long soft magnetic alloys Permanent Magnet travel, and high (e.g. CoNiFe) Synchronous Actuator efficiency using Some varieties (LPMSA), Linear planar also require Reluctance semiconductor permanent magnetic Synchronous Actuator fabrication materials such as (LRSA), Linear techniques Neodymium iron Switched Reluctance Long actuator boron (NdFeB) Actuator (LSRA), and travel is available Requires complex the Linear Stepper Medium force is multi-phase drive Actuator (LSA). available circuitry Low voltage High current operation operation BASIC OPERATION MODE Actuator This is the simplest Simple operation Drop repetition Thermal ink jet directly mode of operation: the No external fields rate is usually Piezoelectric ink pushes ink actuator directly required limited to around 10 kHz. jet supplies sufficient Satellite drops can However, this IJ01, IJ02, IJ03, kinetic energy to expel be avoided if drop is not fundamental IJ04, IJ05, IJ06, the drop. The drop velocity is less than to the method, but is IJ07, IJ09, IJ11, must have a sufficient 4 m/s related to the refill IJ12, IJ14, IJ16, velocity to overcome Can be efficient, method normally IJ20, IJ22, IJ23, the surface tension. depending upon the used IJ24, IJ25, IJ26, actuator used All of the drop IJ27, IJ28, IJ29, kinetic energy must IJ30, IJ31, IJ32, be provided by the IJ33, IJ34, IJ35, actuator IJ36, IJ37, IJ38, Satellite drops IJ39, IJ40, IJ41, usually form if drop IJ42, IJ43, IJ44 velocity is greater than 4.5 m/s Proximity The drops to be Very simple print Requires close Silverbrook, EP printed are selected by head fabrication can proximity between 0771 658 A2 and some manner (e.g. be used the print head and related patent thermally induced The drop the print media or applications surface tension selection means transfer roller reduction of does not need to May require two pressurized ink). provide the energy print heads printing Selected drops are required to separate alternate rows of the separated from the ink the drop from the image in the nozzle by nozzle Monolithic color contact with the print print heads are medium or a transfer difficult roller. Electro- The drops to be Very simple print Requires very Silverbrook, EP static pull printed are selected by head fabrication can high electrostatic 0771 658 A2 and on ink some manner (e.g. be used field related patent thermally induced The drop Electrostatic field applications surface tension selection means for small nozzle Tone-Jet reduction of does not need to sizes is above air pressurized ink). provide the energy breakdown Selected drops are required to separate Electrostatic field separated from the ink the drop from the may attract dust in the nozzle by a nozzle strong electric field. Magnetic The drops to be Very simple print Requires Silverbrook, EP pull on ink printed are selected by head fabrication can magnetic ink 0771 658 A2 and some manner (e.g. be used Ink colors other related patent thermally induced The drop than black are applications surface tension selection means difficult reduction of does not need to Requires very pressurized ink). provide the energy high magnetic fields Selected drops are required to separate separated from the ink the drop from the in the nozzle by a nozzle strong magnetic field acting on the magnetic ink. Shutter The actuator moves a High speed (>50 kHz) Moving parts are IJ13, IJ17, IJ21 shutter to block ink operation can required flow to the nozzle. be achieved due to Requires ink The ink pressure is reduced refill time pressure modulator pulsed at a multiple of Drop timing can Friction and wear the drop ejection be very accurate must be considered frequency. The actuator Stiction is energy can be very possible low Shuttered The actuator moves a Actuators with Moving parts are IJ08, IJ15, IJ18, grill shutter to block ink small travel can be required IJ19 flow through a grill to used Requires ink the nozzle. The shutter Actuators with pressure modulator movement need only small force can be Friction and wear be equal to the width used must be considered of the grill holes. High speed (>50 kHz) Stiction is operation can possible be achieved Pulsed A pulsed magnetic Extremely low Requires an IJ10 magnetic field attracts an ‘ink energy operation is external pulsed pull on ink pusher’ at the drop possible magnetic field pusher ejection frequency. An No heat Requires special actuator controls a dissipation materials for both catch, which prevents problems the actuator and the the ink pusher from ink pusher moving when a drop is Complex not to be ejected. construction AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) None The actuator directly Simplicity of Drop ejection Most ink jets, fires the ink drop, and construction energy must be including there is no external Simplicity of supplied by piezoelectric and field or other operation individual nozzle thermal bubble. mechanism required. Small physical actuator IJ01, IJ02, IJ03, size IJ04, IJ05, IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24, IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The ink pressure Oscillating ink Requires external Silverbrook, EP ink oscillates, providing pressure can ink pressure 0771 658 A2 and pressure much of the drop provide a refill oscillator related patent (including ejection energy. The pulse, allowing Ink pressure applications acoustic actuator selects which higher operating phase and amplitude IJ08, IJ13, IJ15, stimulation) drops are to be fired speed must be carefully IJ17, IJ18, IJ19, by selectively The actuators may controlled IJ21 blocking or enabling operate with much Acoustic nozzles. The ink lower energy reflections in the ink pressure oscillation Acoustic lenses chamber must be may be achieved by can be used to focus designed for vibrating the print the sound on the head, or preferably by nozzles an actuator in the ink supply. Media The print head is Low power Precision Silverbrook, EP proximity placed in close High accuracy assembly required 0771 658 A2 and proximity to the print Simple print head Paper fibers may related patent medium. Selected construction cause problems applications drops protrude from Cannot print on the print head further rough substrates than unselected drops, and contact the print medium. The drop soaks into the medium fast enough to cause drop separation. Transfer Drops are printed to a High accuracy Bulky Silverbrook, EP roller transfer roller instead Wide range of Expensive 0771 658 A2 and of straight to the print print substrates can Complex related patent medium. A transfer be used construction applications roller can also be used Ink can be dried Tektronix hot for proximity drop on the transfer roller melt piezoelectric separation. ink jet Any of the IJ series Electro- An electric field is Low power Field strength Silverbrook, EP static used to accelerate Simple print head required for 0771 658 A2 and selected drops towards construction separation of small related patent the print medium. drops is near or applications above air Tone-Jet breakdown Direct A magnetic field is Low power Requires Silverbrook, EP magnetic used to accelerate Simple print head magnetic ink 0771 658 A2 and field selected drops of construction Requires strong related patent magnetic ink towards magnetic field applications the print medium. Cross The print head is Does not require Requires external IJ06, IJ16 magnetic placed in a constant magnetic materials magnet field magnetic field. The to be integrated in Current densities Lorenz force in a the print head may be high, current carrying wire manufacturing resulting in is used to move the process electromigration actuator. problems Pulsed A pulsed magnetic Very low power Complex print IJ10 magnetic field is used to operation is possible head construction field cyclically attract a Small print head Magnetic paddle, which pushes size materials required in on the ink. A small print head actuator moves a catch, which selectively prevents the paddle from moving. ACTUATOR AMPLIFICATION OR MODIFICATION METHOD None No actuator Operational Many actuator Thermal Bubble mechanical simplicity mechanisms have Ink jet amplification is used. insufficient travel, IJ01, IJ02, IJ06, The actuator directly or insufficient force, IJ07, IJ16, IJ25, drives the drop to efficiently drive IJ26 ejection process. the drop ejection process Differential An actuator material Provides greater High stresses are Piezoelectric expansion expands more on one travel in a reduced involved IJ03, IJ09, IJ17, bend side than on the other. print head area Care must be IJ18, IJ19, IJ20, actuator The expansion may be taken that the IJ21, IJ22, IJ23, thermal, piezoelectric, materials do not IJ24, IJ27, IJ29, magnetostrictive, or delaminate IJ30, IJ31, IJ32, other mechanism. The Residual bend IJ33, IJ34, IJ35, bend actuator converts resulting from high IJ36, IJ37, IJ38, a high force low travel temperature or high IJ39, IJ42, IJ43, actuator mechanism to stress during IJ44 high travel, lower formation force mechanism. Transient A trilayer bend Very good High stresses are IJ40, IJ41 bend actuator where the two temperature stability involved actuator outside layers are High speed, as a Care must be identical. This cancels new drop can be taken that the bend due to ambient fired before heat materials do not temperature and dissipates delaminate residual stress. The Cancels residual actuator only responds stress of formation to transient heating of one side or the other. Reverse The actuator loads a Better coupling to Fabrication IJ05, IJ11 spring spring. When the the ink complexity actuator is turned off, High stress in the the spring releases. spring This can reverse the force/distance curve of the actuator to make it compatible with the force/time requirements of the drop ejection. Actuator A series of thin Increased travel Increased Some stack actuators are stacked. Reduced drive fabrication piezoelectric ink jets This can be voltage complexity IJ04 appropriate where Increased actuators require high possibility of short electric field strength, circuits due to such as electrostatic pinholes and piezoelectric actuators. Multiple Multiple smaller Increases the Actuator forces IJ12, IJ13, IJ18, actuators actuators are used force available from may not add IJ20, IJ22, IJ28, simultaneously to an actuator linearly, reducing IJ42, IJ43 move the ink. Each Multiple actuators efficiency actuator need provide can be positioned to only a portion of the control ink flow force required. accurately Linear A linear spring is used Matches low Requires print IJ15 Spring to transform a motion travel actuator with head area for the with small travel and higher travel spring high force into a requirements longer travel, lower Non-contact force motion. method of motion transformation Coiled A bend actuator is Increases travel Generally IJ17, IJ21, IJ34, actuator coiled to provide Reduces chip area restricted to planar IJ35 greater travel in a Planar implementations reduced chip area. implementations are due to extreme relatively easy to fabrication fabricate. difficulty in other orientations. Flexure A bend actuator has a Simple means of Care must be IJ10, IJ19, IJ33 bend small region near the increasing travel of taken not to exceed actuator fixture point, which a bend actuator the elastic limit in flexes much more the flexure area readily than the Stress distribution remainder of the is very uneven actuator. The actuator Difficult to flexing is effectively accurately model converted from an with finite element even coiling to an analysis angular bend, resulting in greater travel of the actuator tip. Catch The actuator controls a Very low actuator Complex IJ10 small catch. The catch energy construction either enables or Very small Requires external disables movement of actuator size force an ink pusher that is Unsuitable for controlled in a bulk pigmented inks manner. Gears Gears can be used to Low force, low Moving parts are IJ13 increase travel at the travel actuators can required expense of duration. be used Several actuator Circular gears, rack Can be fabricated cycles are required and pinion, ratchets, using standard More complex and other gearing surface MEMS drive electronics methods can be used. processes Complex construction Friction, friction, and wear are possible Buckle A buckle plate can be Very fast Must stay within S. Hirata et al, plate used to change a slow movement elastic limits of the “An Ink-jet Head actuator into a fast achievable materials for long Using Diaphragm motion. It can also device life Microactuator”, convert a high force, High stresses Proc. IEEE MEMS, low travel actuator involved February 1996, pp 418-423. into a high travel, Generally high IJ18, IJ27 medium force motion. power requirement Tapered A tapered magnetic Linearizes the Complex IJ14 magnetic pole can increase magnetic construction pole travel at the expense force/distance curve of force. Lever A lever and fulcrum is Matches low High stress IJ32, IJ36, IJ37 used to transform a travel actuator with around the fulcrum motion with small higher travel travel and high force requirements into a motion with Fulcrum area has longer travel and no linear movement, lower force. The lever and can be used for can also reverse the a fluid seal direction of travel. Rotary The actuator is High mechanical Complex IJ28 impeller connected to a rotary advantage construction impeller. A small The ratio of force Unsuitable for angular deflection of to travel of the pigmented inks the actuator results in actuator can be a rotation of the matched to the impeller vanes, which nozzle requirements push the ink against by varying the stationary vanes and number of impeller out of the nozzle. vanes Acoustic A refractive or No moving parts Large area 1993 Hadimioglu lens diffractive (e.g. zone required et al, EUP 550,192 plate) acoustic lens is Only relevant for 1993 Elrod et al, used to concentrate acoustic ink jets EUP 572,220 sound waves. Sharp A sharp point is used Simple Difficult to Tone-jet conductive to concentrate an construction fabricate using point electrostatic field. standard VLSI processes for a surface ejecting ink- jet Only relevant for electrostatic ink jets ACTUATOR MOTION Volume The volume of the Simple High energy is Hewlett-Packard expansion actuator changes, construction in the typically required to Thermal Ink jet pushing the ink in all case of thermal ink achieve volume Canon Bubblejet directions. jet expansion. This leads to thermal stress, cavitation, and kogation in thermal ink jet implementations Linear, The actuator moves in Efficient coupling High fabrication IJ01, IJ02, IJ04, normal to a direction normal to to ink drops ejected complexity may be IJ07, IJ11, IJ14 chip the print head surface. normal to the required to achieve surface The nozzle is typically surface perpendicular in the line of motion movement. Parallel to The actuator moves Suitable for Fabrication IJ12, IJ13, IJ15, chip parallel to the print planar fabrication complexity IJ33,, IJ34, IJ35, surface head surface. Drop Friction IJ36 ejection may still be Stiction normal to the surface. Membrane An actuator with a The effective area Fabrication 1982 Howkins push high force but small of the actuator complexity U.S. Pat. No. 4,459,601 area is used to push a becomes the Actuator size stiff membrane that is membrane area Difficulty of in contact with the ink. integration in a VLSI process Rotary The actuator causes Rotary levers may Device IJ05, IJ08, IJ13, the rotation of some be used to increase complexity IJ28 element, such a grill or travel May have friction impeller Small chip area at a pivot point requirements Bend The actuator bends A very small Requires the 1970 Kyser et al when energized. This change in actuator to be made U.S. Pat. No. 3,946,398 may be due to dimensions can be from at least two 1973 Stemme differential thermal converted to a large distinct layers, or to U.S. Pat. No. 3,747,120 expansion, motion. have a thermal IJ03, IJ09, IJ10, piezoelectric difference across the IJ19, IJ23, IJ24, expansion, actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33, IJ34, other form of relative IJ35 dimensional change. Swivel The actuator swivels Allows operation Inefficient IJ06 around a central pivot. where the net linear coupling to the ink This motion is suitable force on the paddle motion where there are is zero opposite forces Small chip area applied to opposite requirements sides of the paddle, e.g. Lorenz force. Straighten The actuator is Can be used with Requires careful IJ26, IJ32 normally bent, and shape memory balance of stresses straightens when alloys where the to ensure that the energized. austenic phase is quiescent bend is planar accurate Double The actuator bends in One actuator can Difficult to make IJ36, IJ37, IJ38 bend one direction when be used to power the drops ejected by one element is two nozzles. both bend directions energized, and bends Reduced chip identical. the other way when size. A small efficiency another element is Not sensitive to loss compared to energized. ambient temperature equivalent single bend actuators. Shear Energizing the Can increase the Not readily 1985 Fishbeck actuator causes a shear effective travel of applicable to other U.S. Pat. No. 4,584,590 motion in the actuator piezoelectric actuator material. actuators mechanisms Radial The actuator squeezes Relatively easy to High force 1970 Zoltan U.S. Pat. No. constriction an ink reservoir, fabricate single required 3,683,212 forcing ink from a nozzles from glass Inefficient constricted nozzle. tubing as Difficult to macroscopic integrate with VLSI structures processes Coil/ A coiled actuator Easy to fabricate Difficult to IJ17, IJ21, IJ34, uncoil uncoils or coils more as a planar VLSI fabricate for non- IJ35 tightly. The motion of process planar devices the free end of the Small area Poor out-of-plane actuator ejects the ink. required, therefore stiffness low cost Bow The actuator bows (or Can increase the Maximum travel IJ16, IJ18, IJ27 buckles) in the middle speed of travel is constrained when energized. Mechanically High force rigid required Push-Pull Two actuators control The structure is Not readily IJ18 a shutter. One actuator pinned at both ends, suitable for ink jets pulls the shutter, and so has a high out-of- which directly push the other pushes it. plane rigidity the ink Curl A set of actuators curl Good fluid flow Design IJ20, IJ42 inwards inwards to reduce the to the region behind complexity volume of ink that the actuator they enclose. increases efficiency Curl A set of actuators curl Relatively simple Relatively large IJ43 outwards outwards, pressurizing construction chip area ink in a chamber surrounding the actuators, and expelling ink from a nozzle in the chamber. Iris Multiple vanes enclose High efficiency High fabrication IJ22 a volume of ink. These Small chip area complexity simultaneously rotate, Not suitable for reducing the volume pigmented inks between the vanes. Acoustic The actuator vibrates The actuator can Large area 1993 Hadimioglu vibration at a high frequency. be physically distant required for et al, EUP 550,192 from the ink efficient operation 1993 Elrod et al, at useful frequencies EUP 572,220 Acoustic coupling and crosstalk Complex drive circuitry Poor control of drop volume and position None In various ink jet No moving parts Various other Silverbrook, EP designs the actuator tradeoffs are 0771 658 A2 and does not move. required to related patent eliminate moving applications parts Tone-jet NOZZLE REFILL METHOD Surface This is the normal way Fabrication Low speed Thermal ink jet tension that ink jets are simplicity Surface tension Piezoelectric ink refilled. After the Operational force relatively jet actuator is energized, simplicity small compared to IJ01-IJ07, IJ10-IJ14, it typically returns actuator force IJ16, IJ20, rapidly to its normal Long refill time IJ22-IJ45 position. This rapid usually dominates return sucks in air the total repetition through the nozzle rate opening. The ink surface tension at the nozzle then exerts a small force restoring the meniscus to a minimum area. This force refills the nozzle. Shuttered Ink to the nozzle High speed Requires common IJ08, IJ13, IJ15, oscillating chamber is provided at Low actuator ink pressure IJ17, IJ18, IJ19, ink a pressure that energy, as the oscillator IJ21 pressure oscillates at twice the actuator need only May not be drop ejection open or close the suitable for frequency. When a shutter, instead of pigmented inks drop is to be ejected, ejecting the ink drop the shutter is opened for 3 half cycles: drop ejection, actuator return, and refill. The shutter is then closed to prevent the nozzle chamber emptying during the next negative pressure cycle. Refill After the main High speed, as the Requires two IJ09 actuator actuator has ejected a nozzle is actively independent drop a second (refill) refilled actuators per nozzle actuator is energized. The refill actuator pushes ink into the nozzle chamber. The refill actuator returns slowly, to prevent its return from emptying the chamber again. Positive The ink is held a slight High refill rate, Surface spill must Silverbrook, EP ink positive pressure. therefore a high be prevented 0771 658 A2 and pressure After the ink drop is drop repetition rate Highly related patent ejected, the nozzle is possible hydrophobic print applications chamber fills quickly head surfaces are Alternative for:, as surface tension and required IJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20, operate to refill the IJ22-IJ45 nozzle. METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Long inlet The ink inlet channel Design simplicity Restricts refill Thermal ink jet channel to the nozzle chamber Operational rate Piezoelectric ink is made long and simplicity May result in a jet relatively narrow, Reduces crosstalk relatively large chip IJ42, IJ43 relying on viscous area drag to reduce inlet Only partially back-flow. effective Positive The ink is under a Drop selection Requires a Silverbrook, EP ink positive pressure, so and separation method (such as a 0771 658 A2 and pressure that in the quiescent forces can be nozzle rim or related patent state some of the ink reduced effective applications drop already protrudes Fast refill time hydrophobizing, or Possible operation from the nozzle. both) to prevent of the following: This reduces the flooding of the IJ01-IJ07, IJ09-IJ12, pressure in the nozzle ejection surface of IJ14, IJ16, chamber which is the print head. IJ20, IJ22,, IJ23-IJ34, required to eject a IJ36-IJ41, certain volume of ink. IJ44 The reduction in chamber pressure results in a reduction in ink pushed out through the inlet. Baffle One or more baffles The refill rate is Design HP Thermal Ink are placed in the inlet not as restricted as complexity Jet ink flow. When the the long inlet May increase Tektronix actuator is energized, method. fabrication piezoelectric ink jet the rapid ink Reduces crosstalk complexity (e.g. movement creates Tektronix hot melt eddies which restrict Piezoelectric print the flow through the heads). inlet. The slower refill process is unrestricted, and does not result in eddies. Flexible In this method recently Significantly Not applicable to Canon flap disclosed by Canon, reduces back-flow most ink jet restricts the expanding actuator for edge-shooter configurations inlet (bubble) pushes on a thermal ink jet Increased flexible flap that devices fabrication restricts the inlet. complexity Inelastic deformation of polymer flap results in creep over extended use Inlet filter A filter is located Additional Restricts refill IJ04, IJ12, IJ24, between the ink inlet advantage of ink rate IJ27, IJ29, IJ30 and the nozzle filtration May result in chamber. The filter Ink filter may be complex has a multitude of fabricated with no construction small holes or slots, additional process restricting ink flow. steps The filter also removes particles which may block the nozzle. Small inlet The ink inlet channel Design simplicity Restricts refill IJ02, IJ37, IJ44 compared to the nozzle chamber rate to nozzle has a substantially May result in a smaller cross section relatively large chip than that of the nozzle, area resulting in easier ink Only partially egress out of the effective nozzle than out of the inlet. Inlet A secondary actuator Increases speed of Requires separate IJ09 shutter controls the position the ink-jet print refill actuator and of a shutter, closing head operation drive circuit off the ink inlet when the main actuator is energized. The inlet is The method avoids the Back-flow Requires careful IJ01, IJ03, IJ05, located problem of inlet back- problem is design to minimize IJ06, IJ07, IJ10, behind the flow by arranging the eliminated the negative IJ11, IJ14, IJ16, ink- ink-pushing surface of pressure behind the IJ22, IJ23, IJ25, pushing the actuator between paddle IJ28, IJ31, IJ32, surface the inlet and the IJ33, IJ34, IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the The actuator and a Significant Small increase in IJ07, IJ20, IJ26, actuator wall of the ink reductions in back- fabrication IJ38 moves to chamber are arranged flow can be complexity shut off so that the motion of achieved the inlet the actuator closes off Compact designs the inlet. possible Nozzle In some configurations Ink back-flow None related to Silverbrook, EP actuator of ink jet, there is no problem is ink back-flow on 0771 658 A2 and does not expansion or eliminated actuation related patent result in movement of an applications ink back- actuator which may Valve-jet flow cause ink back-flow Tone-jet through the inlet. NOZZLE CLEARING METHOD Normal All of the nozzles are No added May not be Most ink jet nozzle fired periodically, complexity on the sufficient to systems firing before the ink has a print head displace dried ink IJ01, IJ02, IJ03, chance to dry. When IJ04, IJ05, IJ06, not in use the nozzles IJ07, IJ09, IJ10, are sealed (capped) IJ11, IJ12, IJ14, against air. IJ16, IJ20, IJ22, The nozzle firing is IJ23, IJ24, IJ25, usually performed IJ26, IJ27, IJ28, during a special IJ29, IJ30, IJ31, clearing cycle, after IJ32, IJ33, IJ34, first moving the print IJ36, IJ37, IJ38, head to a cleaning IJ39, IJ40,, IJ41, station. IJ42, IJ43, IJ44,, IJ45 Extra In systems which heat Can be highly Requires higher Silverbrook, EP power to the ink, but do not boil effective if the drive voltage for 0771 658 A2 and ink heater it under normal heater is adjacent to clearing related patent situations, nozzle the nozzle May require applications clearing can be larger drive achieved by over- transistors powering the heater and boiling ink at the nozzle. Rapid The actuator is fired in Does not require Effectiveness May be used succession rapid succession. In extra drive circuits depends with: IJ01, IJ02, of some configurations, on the print head substantially upon IJ03, IJ04, IJ05, actuator this may cause heat Can be readily the configuration of IJ06, IJ07, IJ09, pulses build-up at the nozzle controlled and the ink jet nozzle IJ10, IJ11, IJ14, which boils the ink, initiated by digital IJ16, IJ20, IJ22, clearing the nozzle. In logic IJ23, IJ24, IJ25, other situations, it may IJ27, IJ28, IJ29, cause sufficient IJ30, IJ31, IJ32, vibrations to dislodge IJ33, IJ34, IJ36, clogged nozzles. IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is A simple solution Not suitable May be used power to not normally driven to where applicable where there is a with: IJ03, IJ09, ink the limit of its motion, hard limit to IJ16, IJ20, IJ23, pushing nozzle clearing may be actuator movement IJ24, IJ25, IJ27, actuator assisted by providing IJ29, IJ30, IJ31, an enhanced drive IJ32, IJ39, IJ40, signal to the actuator. IJ41, IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is A high nozzle High IJ08, IJ13, IJ15, resonance applied to the ink clearing capability implementation cost IJ17, IJ18, IJ19, chamber. This wave is can be achieved if system does not IJ21 of an appropriate May be already include an amplitude and implemented at very acoustic actuator frequency to cause low cost in systems sufficient force at the which already nozzle to clear include acoustic blockages. This is actuators easiest to achieve if the ultrasonic wave is at a resonant frequency of the ink cavity. Nozzle A microfabricated Can clear severely Accurate Silverbrook, EP clearing plate is pushed against clogged nozzles mechanical 0771 658 A2 and plate the nozzles. The plate alignment is related patent has a post for every required applications nozzle. A post moves Moving parts are through each nozzle, required displacing dried ink. There is risk of damage to the nozzles Accurate fabrication is required Ink The pressure of the ink May be effective Requires pressure May be used with pressure is temporarily where other pump or other all IJ series ink jets pulse increased so that ink methods cannot be pressure actuator streams from all of the used Expensive nozzles. This may be Wasteful of ink used in conjunction with actuator energizing. Print head A flexible ‘blade’ is Effective for Difficult to use if Many ink jet wiper wiped across the print planar print head print head surface is systems head surface. The surfaces non-planar or very blade is usually Low cost fragile fabricated from a Requires flexible polymer, e.g. mechanical parts rubber or synthetic Blade can wear elastomer. out in high volume print systems Separate A separate heater is Can be effective Fabrication Can be used with ink boiling provided at the nozzle where other nozzle complexity many IJ series ink heater although the normal clearing methods jets drop ejection cannot be used mechanism does not Can be require it. The heaters implemented at no do not require additional cost in individual drive some ink jet circuits, as many configurations nozzles can be cleared simultaneously, and no imaging is required. NOZZLE PLATE CONSTRUCTION Electro- A nozzle plate is Fabrication High Hewlett Packard formed separately fabricated simplicity temperatures and Thermal Ink jet nickel from electroformed pressures are nickel, and bonded to required to bond the print head chip. nozzle plate Minimum thickness constraints Differential thermal expansion Laser Individual nozzle No masks Each hole must be Canon Bubblejet ablated or holes are ablated by an required individually formed 1988 Sercel et al., drilled intense UV laser in a Can be quite fast Special SPIE, Vol. 998 polymer nozzle plate, which is Some control equipment required Excimer Beam typically a polymer over nozzle profile Slow where there Applications, pp. such as polyimide or is possible are many thousands 76-83 polysulphone Equipment of nozzles per print 1993 Watanabe et required is relatively head al., U.S. Pat. No. 5,208,604 low cost May produce thin burrs at exit holes Silicon A separate nozzle High accuracy is Two part K. Bean, IEEE micro- plate is attainable construction Transactions on machined micromachined from High cost Electron Devices, single crystal silicon, Requires Vol. ED-25, No. 10, and bonded to the precision alignment 1978, pp 1185-1195 print head wafer. Nozzles may be Xerox 1990 clogged by adhesive Hawkins et al., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries No expensive Very small nozzle 1970 Zoltan U.S. Pat. No. capillaries are drawn from glass equipment required sizes are difficult to 3,683,212 tubing. This method Simple to make form has been used for single nozzles Not suited for making individual mass production nozzles, but is difficult to use for bulk manufacturing of print heads with thousands of nozzles. Monolithic, The nozzle plate is High accuracy Requires Silverbrook, EP surface deposited as a layer (<1 μm) sacrificial layer 0771 658 A2 and micro- using standard VLSI Monolithic under the nozzle related patent machined deposition techniques. Low cost plate to form the applications using VLSI Nozzles are etched in Existing nozzle chamber IJ01, IJ02, IJ04, litho- the nozzle plate using processes can be Surface may be IJ11, IJ12, IJ17, graphic VLSI lithography and used fragile to the touch IJ18, IJ20, IJ22, processes etching. IJ24, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Monolithic, The nozzle plate is a High accuracy Requires long IJ03, IJ05, IJ06, etched buried etch stop in the (<1 μm) etch times IJ07, IJ08, IJ09, through wafer. Nozzle Monolithic Requires a IJ10, IJ13, IJ14, substrate chambers are etched in Low cost support wafer IJ15, IJ16, IJ19, the front of the wafer, No differential IJ21, IJ23, IJ25, and the wafer is expansion IJ26 thinned from the back side. Nozzles are then etched in the etch stop layer. No nozzle Various methods have No nozzles to Difficult to Ricoh 1995 plate been tried to eliminate become clogged control drop Sekiya et al U.S. Pat. No. the nozzles entirely, to position accurately 5,412,413 prevent nozzle Crosstalk 1993 Hadimioglu clogging. These problems et al EUP 550,192 include thermal bubble 1993 Elrod et al mechanisms and EUP 572,220 acoustic lens mechanisms Trough Each drop ejector has Reduced Drop firing IJ35 a trough through manufacturing direction is sensitive which a paddle moves. complexity to wicking. There is no nozzle Monolithic plate. Nozzle slit The elimination of No nozzles to Difficult to 1989 Saito et al instead of nozzle holes and become clogged control drop U.S. Pat. No. 4,799,068 individual replacement by a slit position accurately nozzles encompassing many Crosstalk actuator positions problems reduces nozzle clogging, but increases crosstalk due to ink surface waves DROP EJECTION DIRECTION Edge Ink flow is along the Simple Nozzles limited to Canon Bubblejet (‘edge surface of the chip, construction edge 1979 Endo et al GB shooter’) and ink drops are No silicon etching High resolution is patent 2,007,162 ejected from the chip required difficult Xerox heater-in- edge. Good heat sinking Fast color pit 1990 Hawkins et via substrate printing requires al U.S. Pat. No. 4,899,181 Mechanically one print head per Tone-jet strong color Ease of chip handing Surface Ink flow is along the No bulk silicon Maximum ink Hewlett-Packard (‘roof surface of the chip, etching required flow is severely TIJ 1982 Vaught et shooter’) and ink drops are Silicon can make restricted al U.S. Pat. No. 4,490,728 ejected from the chip an effective heat IJ02, IJ11, IJ12, surface, normal to the sink IJ20, IJ22 plane of the chip. Mechanical strength Through Ink flow is through the High ink flow Requires bulk Silverbrook, EP chip, chip, and ink drops are Suitable for silicon etching 0771 658 A2 and forward ejected from the front pagewidth print related patent (‘up surface of the chip. heads applications shooter’) High nozzle IJ04, IJ17, IJ18, packing density IJ24, IJ27-IJ45 therefore low manufacturing cost Through Ink flow is through the High ink flow Requires wafer IJ01, IJ03, IJ05, chip, chip, and ink drops are Suitable for thinning IJ06, IJ07, IJ08, reverse ejected from the rear pagewidth print Requires special IJ09, IJ10, IJ13, (‘down surface of the chip. heads handling during IJ14, IJ15, IJ16, shooter’) High nozzle manufacture IJ19, IJ21, IJ23, packing density IJ25, IJ26 therefore low manufacturing cost Through Ink flow is through the Suitable for Pagewidth print Epson Stylus actuator actuator, which is not piezoelectric print heads require Tektronix hot fabricated as part of heads several thousand melt piezoelectric the same substrate as connections to drive ink jets the drive transistors. circuits Cannot be manufactured in standard CMOS fabs Complex assembly required INK TYPE Aqueous, Water based ink which Environmentally Slow drying Most existing ink dye typically contains: friendly Corrosive jets water, dye, surfactant, No odor Bleeds on paper All IJ series ink humectant, and May jets biocide. strikethrough Silverbrook, EP Modern ink dyes have Cockles paper 0771 658 A2 and high water-fastness, related patent light fastness applications Aqueous, Water based ink which Environmentally Slow drying IJ02, IJ04, IJ21, pigment typically contains: friendly Corrosive IJ26, IJ27, IJ30 water, pigment, No odor Pigment may clog Silverbrook, EP surfactant, humectant, Reduced bleed nozzles 0771 658 A2 and and biocide. Reduced wicking Pigment may clog related patent Pigments have an Reduced actuator applications advantage in reduced strikethrough mechanisms Piezoelectric ink- bleed, wicking and Cockles paper jets strikethrough. Thermal ink jets (with significant restrictions) Methyl MEK is a highly Very fast drying Odorous All IJ series ink Ethyl volatile solvent used Prints on various Flammable jets Ketone for industrial printing substrates such as (MEK) on difficult surfaces metals and plastics such as aluminum cans. Alcohol Alcohol based inks Fast drying Slight odor All IJ series ink (ethanol, can be used where the Operates at sub- Flammable jets 2-butanol, printer must operate at freezing and temperatures below temperatures others) the freezing point of Reduced paper water. An example of cockle this is in-camera Low cost consumer photographic printing. Phase The ink is solid at No drying time- High viscosity Tektronix hot change room temperature, and ink instantly freezes Printed ink melt piezoelectric (hot melt) is melted in the print on the print medium typically has a ink jets head before jetting. Almost any print ‘waxy’ feel 1989 Nowak U.S. Pat. No. Hot melt inks are medium can be used Printed pages may 4,820,346 usually wax based, No paper cockle ‘block’ All IJ series ink with a melting point occurs Ink temperature jets around 80° C. After No wicking may be above the jetting the ink freezes occurs curie point of almost instantly upon No bleed occurs permanent magnets contacting the print No strikethrough Ink heaters medium or a transfer occurs consume power roller. Long warm-up time Oil Oil based inks are High solubility High viscosity: All IJ series ink extensively used in medium for some this is a significant jets offset printing. They dyes limitation for use in have advantages in Does not cockle ink jets, which improved paper usually require a characteristics on Does not wick low viscosity. Some paper (especially no through paper short chain and wicking or cockle). multi-branched oils Oil soluble dies and have a sufficiently pigments are required. low viscosity. Slow drying Micro- A microemulsion is a Stops ink bleed Viscosity higher All IJ series ink emulsion stable, self forming High dye than water jets emulsion of oil, water, solubility Cost is slightly and surfactant. The Water, oil, and higher than water characteristic drop size amphiphilic soluble based ink is less than 100 nm, dies can be used High surfactant and is determined by Can stabilize concentration the preferred curvature pigment required (around of the surfactant. suspensions 5%) 

1. An inkjet printhead comprising a substrate having an array of nozzles grouped in nozzle pairs, each nozzle pair having a common nozzle chamber and a single actuator configured to selectively eject ink from one or other of the nozzles in said nozzle pair.
 2. The inkjet printhead of claim 1, wherein each nozzle chamber is in fluid communication with an ink supply channel via an ink inlet defined in said nozzle chamber.
 3. The inkjet printhead of claim 2, wherein said actuator is a moveable actuator configured to cause selective ejection of ink from one or other of the nozzles in a respective nozzle pair while simultaneously causing an inflow of ink from the ink supply channel into the nozzle chamber via the ink inlet.
 4. The inkjet printhead of claim 3, wherein each movable actuator incorporates a thermal bend actuator, the thermal bend actuator being configured to undergo movement due to thermal expansion.
 5. The inkjet printhead of claim 4, wherein each thermal bend actuator comprises a beam supporting a paddle, the beam and paddle being arranged so that movement of the paddle from a quiescent position towards a first nozzle of a respective nozzle pair causes ejection of ink from said first nozzle.
 6. The inkjet printhead of claim 5, wherein the beam comprises a core element sandwiched between a pair of resistive elements such that the paddle is selectively moveable in opposite directions from relative to a quiescent position. 